1. Field of the Invention
The present invention relates to isolated polypeptides having .alpha.-amylase activity and isolated nucleic acid sequences encoding the polypeptides. Further, the invention relates to variants of the .alpha.-amylases of the invention. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the nucleic acid sequences as well as methods for producing and using the polypeptides.
2. Description of the Related Art
For a number of years .alpha.-amylase enzymes have been used for a variety of different purposes, the most important of which are starch liquefaction, textile desizing, starch modification in the paper and pulp industry, and for brewing and baking. A further use of .alpha.-amylases, which is becoming increasingly important is the removal of starchy stains during washing with a detergent at alkaline pH.
Examples of commercial .alpha.-amylase products are Termamyl.RTM., Duramyl.TM., BAN.RTM. and Fungamyl.RTM., all available from Novo Nordisk A/S, Denmark. These and similar products from other commercial sources have an acidic to a neutral pH optimum, typically in the range of from pH 5 to pH 7.5, and they do not display optimal activity in detergent solutions at alkaline pH.
WO 95/26397 discloses an .alpha.-amylase from a Bacillus strain which has optimum activity at pH 8. WO 96/23873 describes variants of Bacillus amylases with improved performance under washing conditions.
U.S. Pat. No. 5,147,796 describes an alkaline pullulanase having alpha-amylase activity. FIG. 2b of the document shows optimum amylase activity at pH 8-8.5.
M. Takagi et al., J. Ferment. Bioeng., vol 81, No. 6, 557-559 (1996) describe an alkaliphilic alpha-amylase-pullulanase from Bacillus sp. The enzyme has optimum amylase activity at pH 9, but the activity drops rapidly at higher pH, and the activity at pH 10 is lower than at pH 7.
WO 97/00324 (KAO) disclose a gene encoding an alkaline liquefying .alpha.-amylase derived from Bacillus sp. strain KSM-AP1378 with the deposited no. FERM BP-3048 suitable for detergents.
It is an object of the present invention to provide novel .alpha.-amylases with improved performance in alkaline solutions, especially in alkaline detergent solutions at pH around 9-11.